The present invention relates to a dispensing device for various liquids, and more particularly to a liquid dispensing device which allows precise control over the amount of liquid dispensed.
Several types of prior art dispensing systems are used for dispensing metered amounts of liquid or paste for a variety of applications. One such application is in the assembly of printed circuit boards and integrated circuit chips, wherein dispensing systems are used in the process of encapsulating integrated circuits with an encapsulant material and in the process of under filling flip integrated circuit chips with an encapsulant. Prior art dispensing systems are also used for dispensing dots or balls of liquid epoxy or solder onto circuit boards and integrated circuits. The liquid epoxy and solder is primarily used to connect components to a circuit board or to connect components within an integrated circuit. The dispensing systems described above include those manufactured and distributed by Camelot Systems, Inc. of Haverhill, Mass., the assignee of the present invention under the name CAM/ALOT(copyright).
In a typical dispensing system, a pump and dispenser assembly is mounted to a moving assembly for moving the pump and dispenser assembly along three mutually orthogonal axes (x, y, z), by servomotors controlled by a computer system or controller. To dispense a volume of liquid on a circuit board or some other substrate at a desired location, the pump and dispenser assembly is moved along the horizontal x and y axes until it is located over the desired location. The pump and dispenser assembly is then lowered along the vertical z axis until the nozzle is at an appropriate height over the substrate. The pump and dispenser assembly dispenses a predetermined volume of liquid, is then raised along the z axis, moved along the x and y axes to a next desired location, and is lowered along the vertical z axis to dispense the predetermined volume of liquid at the next location.
In dispensing applications such as those described above, the accuracy of the volume of liquid dispensed by the system is an important feature of the system. In one prior art dispensing system, the pump and dispenser assembly includes an auguring screw housed in an auguring chamber within a dispenser housing. The auguring screw is rotated within the chamber to provide a controlled amount of liquid. The pump and dispenser assembly has a nozzle for dispensing material onto a substrate. The liquid to be dispensed by the pump and dispenser assembly is contained in a vertical, cylindrical syringe coupled to the dispenser housing by a bracket. The syringe has a top piece having clamps that provide a pressure tight seal between the syringe and the top piece. The top piece includes an adapter for coupling to an air line to receive pressurized air. The pressurized air is used to force the dispensing material from the syringe into the pump and dispenser assembly.
The prior art dispensing systems described above are effective in dispensing material onto a substrate, however, it is desirable to have a dispensing system having greater precision in controlling the amount of material to be dispensed.
Embodiments of the present invention provide an apparatus and method for dispensing a controlled amount of material onto a substrate.
In accordance with one embodiment of the present invention, a liquid dispensing system includes a material control device which cooperates with a switching device and a sealing device contained within a standard dispensing chamber. A standard power control system, such as a servomotor, in communication with the material control device, is used to selectively adjust the position of the material control device to dispense a controlled amount of material. When the sealing device is in a first position and the material control device is compressed a predetermined amount, a vacuum is created which draws material into the dispensing chamber. The material remains within the dispensing chamber as the sealing device in the first position seals an opening leading to a dispensing tip. After a predetermined amount of material is drawn into the dispensing chamber, the switching device moves the sealing device to a second position. This creates a seal to prevent further material from entering into the dispensing chamber. In this second position, the sealing device allows material to exit through the opening at the dispensing tip. By expanding the material control device, the material within the dispensing chamber is forced out the opening of the dispensing tip. In this manner, the precise amount of material to be dispensed onto the substrate can be controlled.
In another embodiment, the material control device includes a screw and piston system. The piston has an opening in one portion thereof to be received by the screw by corresponding engagement teeth. As the piston mates with the screw, it is drawn away from the dispensing chamber. The screw can be disengaged from the piston by a reverse turning action on the screw.
In another embodiment, the switching device is a pneumatic cylinder which is connected to the head of the sealing device which may protrude from the dispensing device.
In another embodiment, the dispensing device includes a retainer, having tapered edges to meet and seal with a first sealing portion of the sealing device when the sealing device is in the first position.
In another embodiment of the present invention, the switching device has a failsafe position to prevent material from leaking from the dispensing device by ensuring that the sealing device remains in a closed position over the dispensing tip.
In yet another embodiment, an adjustment means is provided at the base of the dispensing chamber which allows for adjustment of the length of the opening for the dispensing tip.
Another embodiment of the present invention is directed to a dispensing system for dispensing a quantity of material. The dispensing system includes an inlet port to receive material, an outlet port from which the material is dispensed from the dispensing system, a housing including an inner chamber having an adjustable volume, and a first valve operable in one of an open mode of operation and a closed mode of operation. The first valve is disposed between the inlet port and the inner chamber in such a manner that when the first valve is operating in the open mode, material may flow from the inlet port into the inner chamber, and when the first valve is operating in the closed mode, material is prevented from flowing from the inlet port into the inner chamber. The dispensing system further includes a second valve operable in one of an open mode of operation and a closed mode of operation. The second valve is disposed between the outlet port and the inner chamber in such a manner that when the second valve is operating in the open mode, material may flow from the inner chamber to the outlet port, and when the second valve is operating in the closed position, material is prevented from flowing from the inner chamber to the outlet port.
In one embodiment, the first valve is constructed and arranged such that the mode of operation of the first valve is controlled in part based on a difference in pressure of material being received in the inlet port and pressure of material in the inner chamber, and the second valve is constructed and arranged such that the mode of operation of the second valve is controlled in part based on a difference in pressure of material in the inner chamber and ambient air pressure at the outlet port.
In still another embodiment, the first valve includes a first spring providing a spring force that causes the first valve to operate in the closed mode of operation unless the pressure of the material in the inlet port is greater than the sum of pressure provided by the spring force and the pressure of material in the inner chamber, and the second valve includes a second spring providing a spring force that causes the second valve to operate in the closed mode of operation unless the pressure of the material in the inner chamber is greater than the sum of pressure provided by the spring force of the second spring and the ambient air pressure at the outlet port.
In still another embodiment, the housing of the dispensing system includes a piston and a ball screw coupled to the piston. The piston is movable within the inner chamber to vary the volume of the inner chamber.
In yet another embodiment, the dispensing system further includes a motor coupled to the ball screw through a coupling nut to control a position of the ball screw and to thereby control a position of the piston in the inner chamber.
In another embodiment, the dispensing system further includes a syringe containing material to be dispensed by the dispensing system, and a syringe cover that provides pressure to the material in the syringe to cause the material to flow out of the syringe and into the inlet port of the dispensing system.
In another embodiment of the present invention, a dispensing system for dispensing a quantity of material includes an inlet port to receive material, an outlet port from which the material is dispensed from the dispensing system, a housing including an inner chamber, means for decreasing air pressure within the inner chamber to fill the inner chamber with material through the inlet port, and means for increasing pressure on the material in the inner chamber to force material from the inner chamber to dispense the material onto a substrate.
Another embodiment of the present invention is directed to a method of dispensing material in a dispensing system. The dispensing system has an inlet port to receive material, an outlet port from which the material is dispensed from the dispensing system, and a housing including an inner chamber. The method includes steps of decreasing air pressure within the inner chamber to cause material to flow through the inlet port into the inner chamber, and increasing pressure on the material in the inner chamber to cause material to flow from the inner chamber through the outlet port to be dispensed by the dispensing system.